As a means for preventing forgery or illicit duplication of an object, it has been proposed, for instance, to record a unique physical property of the object as data in advance, and to match the recorded data with the actual physical property of the object when the authenticity of the object is required to be verified. However, this cannot totally prevent an illicit duplication of the object by analyzing the physical property and duplicating the physical property.
According to a conventional security system, signature data is generated from original data by using a signature generating rule, and the authenticity of the original data is determined by verifying the signature data by using a signature verifying rule. The person who knows the signature verifying rule can verify the authenticity of the original data by verifying the signature data. Also, only the person who knows the signature generating rule can create his own signatured data, and change it. Because this system allows the authenticity of the data to be determined in an effective manner, there have been some attempts to affix a recording medium of the data in the form of a seal onto an object as a proof of the authenticity of the object.
However, even this system cannot totally prevent an attempt to forge the data by illicitly obtaining samples of signatured data and original data, and analyzing the data so as to decipher the signature generating rule and newly create signatured data.